Conventional tester valves, such as the Select Tester® Valve commercially offered by Halliburton Energy Services, Co., utilize a pressure relief valve in the power piston to control whether the annulus pressure application is considered to be a normal opening pressure or a Lock Open operating pressure. For example, in conditions of 12,000 psi hydrostatic pressure and 300° F., the normal operating pressure is approximately 1400 psi and the Lock Open pressure is roughly 1300 psi higher at 2700 psi.
Such designs can be problematic. For example, the pressure relief valve in the power piston is normally in the range of about 1250 psi. Thus, if the ball valve has high friction due to wear or high pressure differential, the pressure required to open the ball valve and unlatch the collets at the same time, could exceed the 1250 pressure relief in the piston. Therefore, instead of the ball valve opening, the tester valve will index forward into the Lock Open position. Ultimately, when the annulus pressure is bled off, the ball valve will still be closed; but, the selector will be in the Lock Open position. If this is the case, the operator will think the valve is normally closed when, actually, it never opened but, instead, has indexed to the Lock Open position.
Moreover, if the friction on the ball mechanism is between the 1250 psi pressure relief pressure and the applied operating pressure, the ball can be opened after the tool has indexed forward. When the annulus pressure is released, the tool will again be unexpectedly in the Locked Open position. Therefore, without ever going above the normal operating pressure, it is possible to put the tool in the Locked Open position. If the tester valve is being utilized to perform a downhole closure, it will not close. If an emergency happens and the tester valve is expected to close in the well downhole, again, it will not. It will require a pressure cycle to the high Lock Open value to return the tool to normal functioning. Such an operation may take 30 minutes minimum to perform.
Accordingly, in view of the foregoing, there is a need in the art for a tester valve having a pressure relief valve that is only active when the ball valve is in the open position. Therefore, if high pressure is required to get the ball open, the ball must open before the pressure relief valve can open and place the tool in the Lock open position. Such a tool would avoid inadvertent Lock Open positions whereby the operator believes that bleeding off the annulus pressure will close the ball, when in fact the tool is in the Locked Open position.